When judging and assessing beer, there are many factors to consider. Principle among them are bitterness, the variety of flavours present in the beverage, along with their intensity, alcohol content, and colour. Standards for those characteristics allow a more uniform determination to be made on the overall quality of any beer.
"Degrees Lovibond" or "°L" scale is a measure of the colour of a substance, usually beer, whiskey, or sugar solutions. The determination of the degrees lovibond takes place by comparing the colour of the substance to a series of amber to brown glass slides, usually by a colorimeter. The scale was devised by Joseph Williams Lovibond. The Standard Reference Method (SRM) and European Brewery Convention (EBC) methods have largely replaced it, with the SRM giving results approximately equal to the °L.
The Standard Reference Method or SRM  is a system modern brewers use to measure colour intensity, roughly darkness (but see Tristimulus Colour below), of a beer or wort. The method involves the use of a spectrophotometer or photometer to measure the attenuation of light of a particular wavelength, 430 nanometers, as it passes through a sample contained in a cuvette located in the light path of the instrument.
The EBC convention also measures beer and wort colour, as well as quantifying turbidity (also known as haze) in beer.
- Color based on Standard Reference Method (SRM)
|2||Pale lager, Witbier, Pilsener, Berliner Weisse||4|
|3||Maibock, Blonde Ale||6|
|6||American Pale Ale, India Pale Ale||12|
|10||English Bitter, ESB||20|
|13||Biere de Garde, Double IPA||26|
|17||Dark lager, Vienna lager, Marzen, Amber Ale||33|
|20||Brown Ale, Bock, Dunkel, Dunkelweizen||39|
|24||Irish Dry Stout, Doppelbock, Porter||47|
|35||Foreign Stout, Baltic Porter||69|
The "Plato scale" is an empirically derived hydrometer scale to measure density of beer wort in terms of percentage of extract by weight. It was developed in 1843 by Bohemian scientist Karl Balling as well as Simon Ack, and improved by German Fritz Plato. The scale expresses the density as the percentage of sucrose by weight, so a wort measured at 12° Plato has the same density as a water−sucrose solution containing 12% sucrose by weight, denoted as 12% Brix. For the brewer, it has an advantage over specific gravity in that it expresses the measurement in terms of the amount of fermentable materials. Degrees Plato are more popular in central European brewing, and occasionally feature in beer names.
The relationship between degrees Plato and specific gravity (SG) is not linear, but a good approximation is that 1° Plato equals four “brewer’s points” (4 x .001); thus 12° Plato corresponds to an SG of 1.048 [1+(12 x 4 x .001)]. Gravity refers to the specific gravity of the wort or must at various stages in the fermentation. This article focuses primarily on the brewing industry. The concepts and equations are basically the same in the wine making industry.
At various stages in alcohol fermentation, the density of the wort varies. Depending upon the depth that the hydrometer falls into the wort, the percentage of alcohol can be determined. Initially (before alcohol production by the yeast commences) the specific gravity of a wort is dependent mostly on the amount of sugar present and, therefore, specific gravity readings can be used to determine sugar content by the use of formulae or tables. This sugar content is expressed in units of grams of sugar per 100 grams of wort equivalent to % w/w and called, in the brewing industry, "degrees Plato" (abbreviated °P) and in the wine industry "degrees Brix". Even when specified in terms of °P it is not uncommon to refer to the pre-fermentation reading as the "Original Gravity", (abbreviated OG) though it is more correct to term it the "Original Extract" (abbreviated OE). It is, of course, correct to refer to the original specific gravity reading as the OG. By considering the original sugar content the brewer or vintner obtains an indication as to the probable ultimate alcoholic content of his product. The OE is often referred to as the "size" of the beer and is, in Germany, often printed on the label as Stammwürze or sometimes just as a percent. In the Czech Republic, for example, they speak of "10 degree beers", "12 degree beers" and so on.
As fermentation progresses the yeast convert sugars to carbon dioxide, ethanol, more yeast and flavour-producing compounds. The decline in the sugar content and the presence of ethanol (which is appreciably less dense than water) both contribute to a lowering in the specific gravity of the wort so that the formulae relating sugar content and specific gravity no longer apply. Nevertheless, by monitoring the decline in SG over time the brewer obtains information about the health and progress of the fermentation and determines that it is complete when gravity stops declining. A gravity measurement taken at this time compared to the original gravity reading can be used to estimate the amount of sugar consumed and thus the amount of ethanol produced. Specific gravity is measured by a hydrometer, pycnometer or oscillating U-tube electronic meter.
Gravity measurements are used to determine the "size" of the beer, its alcoholic strength and how much of the available sugar the yeast were able to consume (a given strain can be expected, under proper conditions, to ferment a wort of a particular composition to within a range of attenuation, that is, they should be able to consume a known percentage of the extract).
Alcohol by volume (abbreviated as abv or ABV) is a standard measure of how much alcohol (ethanol) is contained in an alcoholic beverage (expressed as a percentage of total volume). The abv standard is used worldwide.
The letter "X" is used on some beers, and was traditionally a mark of beer strength, with the more Xs the greater the strength. Some sources suggest that the origin of the mark was in the breweries of medieval monasteries Another plausible explanation is contained in a treatise entitled "The Art of Brewing" published in London in 1829. It says; "The duties on ale and beer, which were first imposed in 1643... at a certain period, in distinguishing between small beer and strong, all ale or beer, sold at or above ten shillings per barrel, was reckoned to be strong and was, therefore, subjected to a higher duty. The cask which contained this strong beer was then first marked with an X signifying ten; and hence the present quack-like denominations of XX (double X) and XXX (treble X) on the casks and accounts of the strong-ale brewers".
In mid-19th century England, the use of "X" and other letters had evolved into a standardised grading system for the strength of beer. Today, it is used as a trade mark by a number of brewers in the United Kingdom, the Commonwealth and the United States.
European Bitterness Units scale, often abbreviated as EBU, is a scale for measuring the perceived bitterness of beer, with lower values being generally "less bitter" and higher values "more bitter". The scale and method are defined by the European Brewery Convention, and the numerical value should be the same as of the International Bitterness Units scale (IBU), defined in co-operation with the American Society of Brewing Chemists. However, the exact process of determining EBU and IBU values differs slightly, which may in theory result with slightly smaller values for EBU than IBU.
The International Bittering Units scale, or simply IBU scale, provides a measure of the bitterness of beer, which is provided by the hops used during brewing. Bittering units are measured through the use of a spectrophotometer and solvent extraction.
This technique was adopted at the same time as another method based on measuring the concentration (in milligrams per liter; parts per million w/v) of isomerized α acids in a beer, causing some confusion among small-scale brewers. The American Society of Brewing Chemists, in the introduction to its methods on measuring bitterness, points out some differences between the results of the two methods:
While the results of the IAA [isomerized α acids] methods are practically identical to those obtained by the [I]BU method for beer brewed with fresh hops, the IAAs of beer brewed with old or poorly stored hops, and with certain special hop extracts, can be significantly lower than the [I]BU figure.—
The bittering effect is less noticeable in beers with a high quantity of malt, so a higher IBU is needed in heavier beers to balance the flavor. For example, an Imperial Stout may have an IBU of 50, but will taste less bitter than an English Bitter with an IBU of 30, because the latter beer uses much less malt than the former. The technical limit for IBU's is around 100; some have tried to surpass this number, but there is no real gauge after 100 IBUs when it comes to taste threshold. Light lagers without much bitterness will generally have 5 IBUs, while a souped-up India Pale Ale may have 100 IBUs or more.
Automated combined systems
For high-through-put applications (as in quality control labs of big breweries for example), automated systems are available. Simple systems work with adjustment data blocks for each kind of beer, high-end systems are matrix-independent and give correct results for e.g. alcohol strength, extract content, pH, color, turbidity, CO2 and O2 without any product-specific calibration.
Latest innovations are packaged beverage analyzers, that measure directly out of the package (glass bottle, PET bottle or can) and give several parameters in one measuring cycle without any sample preparation (no degassing, no filtering, no temperature conditioning).
Oxidative degradation measurement
Oxidative deterioration of beer can be measured by the way of chemiluminescence or by electron spin resonance. Automated systems exist to determine the lag time of beer related to the antioxidant capacity to resist oxidative spoilage of flavors.
- Article at BrewWiki.com
- "Beer 10-A Spectrophotometric Color Method", ASBC Methods of Analysis
- "Lafayette Brewing Co. Beer Terms". www.lafayettebrewingco.com. Archived from the original on 25 July 2008. Retrieved 2008-07-05.
- "Glossary of whisky and distillation". www.celtic-whisky.com. Archived from the original on 5 July 2008. Retrieved 2008-07-05.
- "English Ales Brewery Monterey British Brewing Glossary". www.englishalesbrewery.com. Archived from the original on 4 July 2008. Retrieved 2008-07-05.
- "Frequently Asked Questions - CAMRA". www.camra.org.uk. Retrieved 2008-07-05.
- "Joseph Louis Gay-Lussac (1778–1850)". chemistry.about.com. Retrieved 2008-07-05.
- Beer: Health and Nutrition, Charles W. Bamforth, Blackwell Science Ltd 2004 ISBN 0-632-06446-3 p.34
- The Art of Brewing (Published under the superintendance of the Society for the Diffusion of Useful Knowledge), Baldwin & Craddock, London 1829 p.2
- [Valley Homebrewers] (2007). "Beer and Brewing Glossary". Retrieved 2009-08-05. "IBUs (International Bittering Units) - The accepted worldwide standard for measuring bitterness in beer, also known as EBU, based on the estimated alpha acid percentage of the hops used and the length of time they are boiled."
- [Brewery Convention]. "The Analysis Committee". Retrieved 2009-08-05. "The EBC Analysis Committee also works closely together with the 'American Society of Brewing Chemists' (ASBC) to establish so-called 'International methods' with world-wide recognition of applicability. A partnership declaration between EBC and ASBC has been signed. The integration of the IOB methods of analysis and EBC methods is nearing completion."
- ajdelange (2009-06-11). "Difference between IBU and EBU". Retrieved 2009-08-05. "Because the absorption decreases pretty quickly with time at the completion of extraction the EBC reported value will, in general, be a little smaller than ASBC reported value unless the beer requires centrifugation. For all practical considerations the two systems should give the same results."
- "Beer Bitterness (Beer-23)". Methods of Analysis. American Society of Brewing Chemists. 1996. pp. Beer–23:1–4. Unknown parameter
- "What Is an IBU…Really?". Basic Brewing Radio. Season 4. Episode 12. 2008-03-20.
- Andy Crouch (2006-05-31). The Good Beer Guide to New England. books.google.co.uk. ISBN 9781584654698. Retrieved 2010-07-10.
- "Anton Paar". www.anton-paar.com.
- Detection of Chemiluminescence Produced during Beer Oxidation. Hirotaka Kaneda, Yukinobu Kano, Minoru Kamimura, Toshihiko Osawa and Shunro Kawakishi, Journal of Food Science, May 1990, Volume 55, Issue 3, pages 881–882, doi:10.1111/j.1365-2621.1990.tb05260.x
- Detection of Free Radicals in Beer Oxidation. Hirotaka Kaneda, Yukinobu Kano, Toshihiko Osawa, Narasimhan Ramarathnam, Shunro Kawakishi and Kozo Kamada, Journal of Food Science, May 1988, Volume 53, Issue 3, pages 885–888, doi:10.1111/j.1365-2621.1988.tb08978.x
- Explanation from Brew Your Own
- How To Brew: Hop Bittering Calculations
- Color Measurement
- Systems for Alcohol, Density, pH, Color, Turbdiity, CO2, O2 and many more